Multilayer films have been made for a number of purposes. A heat-shrinkable multilayer film for primal meat packaging is described in U.S. Pat. No. 4,714,638. This film has a barrier layer of vinylidene chloride-methyl acrylate copolymer, and outer layers of ethylene-vinyl acetate copolymer.
A heat-shrinkable laminate film having gas-barrier properties as well as oil resistance properties is described in U.S. Pat. No. 4,547,433. These properties are provided by a film having as the core layer a copolymer of vinylidene chloride or a copolymer of ethylene and vinyl alcohol, and a first outer layer of a copolymer of ethylene and an alpha olefin or a blend of such copolymer with a major proportion of a copolymer of ethylene and vinyl acetate, with a second outer layer of similar composition that has been cross-linked using ionizing radiation, and adhesive layers used to bond the outer layers to the core layer.
Another barrier layer film is described in U.S. Pat. No. 4,778,715, the film having a layer of vinylidene chloride copolymer adhered to a layer comprising a blend of ethylene-butyl acrylate copolymer with linear ethylene-alpha olefin copolymer.
Additionally, U.S. Pat. No. 4,681,797 described a thermoformable, multi-layer plastic sheet with gas barrier properties made up of an inner gas barrier layer, such as vinylidene chloride-vinyl chloride copolymer faced on both sides with a glue layer and surrounded by polyolefin layers.
There is a need for a coextruded film that provides a gas barrier and is also resistant to burning, or is self-extinguishing, and is useful in making a protective laminate film. As may be seen, none of the foregoing provides such combination of properties.
U.S. Pat. No. 4,975,316, issued Dec. 4, 1990, discloses a fire retardant barrier structure in the form of a laminate structure, but does not claim the coextruded barrier film forming a part of the laminate, the barrier in the film being a Saran layer surrounded by outer layers of low density polyethylene.